The term "standard resistance" or "standard running resistance" is herein used to mean any force which opposes the motion of an automotive vehicle which is driven to keep rolling over the surface of a flat road having 0% gradient at a constant vehicle speed. The term "running resistance" is herein used to mean any force which opposes the motion of an automotive vehicle which is driven to keep rolling over the surface of a road at a constant vehicle speed. Running resistance is equal to standard resistance if an automotive vehicle is driven to keep rolling over the surface of a flat road having 0% gradient at a constant vehicle speed. Running resistance increases and becomes greater than standard resistance if the automotive vehicle is accelerated to increase speed from the constant vehicle speed. The term "acceleration resistance" is herein used to mean this increment or difference in running resistance that has occurred due to acceleration. Running resistance is greater when the automotive vehicle is driven to keep rolling over the surface of a flat road having gradient greater than 0% at a constant vehicle speed than standard resistance for the same vehicle speed. The term "gradient resistance" is used to mean this increment or difference in running resistance.
JP-A 9-242862 discloses a driving force control system in which a speed ratio between an input shaft and an output shaft of an automatic transmission is controlled in response to road gradient, throttle opening degree, and vehicle speed. In order to estimate road gradient of a road, over which the vehicle is rolling, a road gradient torque (T.alpha.) is determined by subtracting from a driving torque (To) a sum of a flat road running resistance torque (Tr) and an acceleration resistance torque (T.alpha.). A characteristic of variation of flat road running resistance torque (Tr) against variation of vehicle speed is mapped. This mapped data are retrieved using a current reading point of vehicle speed to give a value of flat road running resistance torque (Tr).
JP-A 7-174042 discloses a driving torque control system for an automotive vehicle. This system adjusts a torque control element of an internal combustion engine in such a direction as to decrease a difference between an estimated driving torque and a target driving torque. Calculating product of an engine torque, a stall torque ratio of a torque converter, and a gear ratio of an automatic transmission gives the estimated driving torque. Retrieving a predetermined map gives the target driving torque against running condition of the vehicle. If there remains a portion of the difference between the estimated driving torque and the target driving torque, a braking torque is applied to cause a reduction in driving torque to assist in decreasing the estimated driving torque toward the target driving torque.